Dental adhesive compositions are generally known in the art. Those compositions are typically used for bonding dental restorative compositions to the surface of hard dental tissue, e.g. the surface of a prepared tooth cavity.
Dental adhesive compositions are often light curable and thus contain the respective initiator components. The dental compositions are typically provided to the dental practitioner in an application device, such as a vial.
The instruction of use often requests the dental practitioner to store the dental adhesive composition in a fridge. Otherwise, the storage stability given by the manufacturer cannot be guaranteed.
Dental adhesive compositions typically contain a variety of components, each of which may have an influence on the storage stability.
Sometimes the initiator components contained in the adhesive composition are assumed to be critical for storage stability.
In this respect JP 2006/111584 (Tokuyama) describes a dental curable composition comprising a chemical polymerization initiator system comprising an aryl borate salt, an acid and a monomer having low solubility to the aryl borate salt.
Other efforts are more concentrated on improving the device for storing the adhesive composition.
In this respect US 2010/075276 (Shofu) describes a storage container for a dental adhesive, comprising an elongated container portion that can store a liquid therein, wherein one end surface of said container portion has a discharge port communicating with an outside, the other end surface of said container portion is closed by a bottom wall, and a tail portion is formed protruding from said bottom wall to the side opposite from the discharge port.
Other efforts are more concentrated on adjusting the molecular structure of the polymerizable components contained in the adhesive composition.
In this respect WO 2009/027005 (Dentsply) suggests a hydrolysis-stable polymerizable monomers having a particular formula.
In contrast to this US 2010/024683 (Mitsui) is more focusing on the acidic components contained in the dental composition. In this respect a phosphate compound is described comprising an unsaturated double bond represented by a particular formula.
WO 00/69394 (3M) relates to a stable one-part dental material comprising a) resin comprising a mono-acid compound having a molecular weight between about 80-5,000, said compound comprising only one acid functionality and further comprising at least one polymerizable functionality b) a fluoride source containing polyvalent metal ions and c) photopolymerization initiator, said composition being free of a storage stability-deleterious amount of a compound having more than one acid functionality.
U.S. Pat. No. 3,853,962 (Gander) relates to dental restorative cements comprising the methacrylate monomer 1,3-bis [2-,3-di(methacryloxy)-propoxy]-benzene. Restorative compositions containing this kind of monomer are said to have improved compressive strength and related physical properties.
US 2003/0167968 (Erdman et al.) relates to dental materials which contain hydrolysis-resistant phosphonic acids with ethylenically unsaturated double bonds and which are especially suitable for use as adhesion promoters.
U.S. Pat. No. 4,539,382 (Omura et al) describes a method of restoring a carious tooth, the method comprising applying to the wall surface of a cavity in a carious tooth an adhesive composition comprising a certain amount of a certain polymerizable monomer, a certain amount of a copolymerizable vinyl monomer and a certain amount of a curing agent, and filling said cavity with a dental filling composition.
US 2011/0315928 A1 (Jin at al.) relates to a low viscosity and low stress dental composition comprising at least one low stress polymerizable resin and at least one filler. The dental composition are said to have high depth of cure and self-leveling characteristics and are capable of bulk application.
WO 2012/106083 A1 (3M) relates to a dental composition comprising a certain compound (A), a filler (B), and an initiator (C), wherein compound (A) comprises a certain backbone unit and one or two spacer units having a certain structure.
Thus, there is still room for improvement especially with regard to the requirements to be fulfilled with respect to modern dental materials.
Dentists still have a demand for long lasting bondings with reliable physical properties. The practitioner in particular is also interested in storage stable compositions.
Adhesive composition described in the prior art, however, are often inferior with respect to storage stability. In particular, it was found that the adhesive strength values often drop over time, i.e. after having stored the composition for a certain period of time.